System and method for improving data transmission

ABSTRACT

Systems and methods for improving data transmission are presented in which predefined masks are selected as a function of line conditions. The predefined masks may be time-frequency masks or power spectral density (PSD) masks. The predefined masks may be static masks, which do not adaptively change as a function of changing line conditions, or adaptive masks, which adaptively change as a function of changing line conditions. Sub-carriers are loaded with data as a function of the selected predefined mask.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. provisional patent application serial Nos. 60/338,939, dated Dec. 10, 2001; 60/341,654, dated Dec. 16, 2001; 60/346,809, dated Jan. 7, 2002; 60/348,575, dated Jan. 14, 2002; 60/350,552, dated Jan. 22, 2002; 60/353,880, dated Feb. 2, 2002; 60/354,888, dated Feb. 6, 2002; and 60/355,117, dated Feb. 8, 2002. These U. S. provisional patent applications are incorporated herein by reference as if set forth in their entireties.

[0002] Co-pending U.S. patent application Nos. 060706-1550 (EL 891429200 US) and 060706-1570 (EL 891429213 US), both mailed on Dec. 10, 2002, are also incorporated herein by reference as if set forth in their entireties.

FIELD OF INVENTION

[0003] The present invention relates generally to data communication and, more particularly, to systems and methods for improving data transmission.

BACKGROUND

[0004] Industries related to modern communication systems have experienced a tremendous growth due to the increasing popularity of the Internet. Digital subscriber line (DSL) technology is one technology that has developed in recent years in response to the demand for high-speed Internet access. DSL technology uses a communication line of a pre-existing telephone system as the backbone for the DSL lines. Thus, both plain old telephone systems (POTS) and DSL systems share a common line for DSL-compatible customer premises. Similarly, other services such as time compression multiplexing (TCM) integrated services digital network (ISDN) can also share a common line with DSL and POTS.

[0005] POTS services and DSL services are deployed on non-overlapping portions of available bandwidth on the communication line. Thus, there is very little concern of cross-talk or other interference between POTS services and DSL services. However, DSL and TCM-ISDN often share a portion of the available bandwidth, thereby making DSL services susceptible to cross-talk from TCM-ISDN services, and vice versa.

[0006] To compound problems even further, system requirements (e.g., the degree of permissible disruption of TCM-ISDN service caused by DSL service) may vary greatly from country to country. For example, Japan may have a greater limitation than the United States on how much disruption is tolerable between concurrently-deployed services on the same line. Thus, acceptable power levels for signal transmission in the United States may be unacceptable for signal transmission in Japan.

[0007] Certain standards committees, such as the International Telecommunication Union-Telecommunication Standardization Sector (ITU-T), have provided standards documents for deployment of DSL, such as G.992.2, “Splitterless Asymmetric Digital Subscriber Line (ADSL) Transceivers” (hereinafter “ITU-T G.992.2”), published in June of 1999. These standards documents provide static power spectral density (PSD) masks that limit the amount of power allocated to the DSL bandwidth, thereby limiting the amount of cross-talk induced by the DSL system on other services concurrently deployed on the same line.

[0008] Given many different static PSD masks, operating parameters of modems may be adjusted by the selection of a particular static PSD mask that is configured for a particular line condition. The selection of the particular static PSD mask, however, is done at the network management level, and typically requires a costly procedure from the Telco to provide physical layer information that also includes information on concurrently-deployed services. In this regard, a digital subscriber line (DSL) service provider may be required to select sub-optimal modem parameters due to the limitations provided at the network management level. The selection of the sub-optimal modem parameters results in sub-optimal performance of the modem.

[0009] Given this deficiency, heretofore-unaddressed needs exist in the industry.

SUMMARY

[0010] The present invention provides systems and methods for improving data transmission.

[0011] Briefly described, in architecture, one embodiment of the system comprises predefined masks, a receiver, and logic configured to select one of the predefined masks. The receiver is configured to receive a signal from a communication line. The signal has information indicative of line conditions. The logic selects one of the predefined masks in response to the received signal from the communication line.

[0012] The present invention can also be viewed as providing methods for improving data transmission. In this regard, one embodiment of the method comprises the steps of receiving a signal having information indicative of line conditions, and selecting a predefined mask in response to the received signal.

[0013] Other systems, methods, features, and advantages of the present invention will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Many aspects of the invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

[0015]FIG. 1 is a block diagram showing an asymmetric digital subscriber line (ADSL) environment in accordance with one embodiment of the invention.

[0016]FIG. 2 is a block diagram showing the ADSL modem of FIG. 1 in greater detail.

[0017]FIG. 3 is a block diagram showing the encoder and gain scaler of FIG. 2 in greater detail.

[0018]FIGS. 4A through 7 are diagrams showing various embodiments of time-frequency masks that may be used by the processor of FIG. 3 in accordance with various embodiments of the invention.

[0019]FIGS. 8 through 18 are diagrams showing various power spectral density (PSD) masks that may be used by the processor of FIG. 3 in accordance with various embodiments of the invention.

[0020]FIG. 19 is a flowchart showing method steps in accordance with one embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Having summarized various aspects of the present invention, reference is now made in detail to the description of the embodiments as illustrated in the drawings. While several embodiments are described in connection with these drawings, there is no intent to limit the invention to the embodiment or embodiments disclosed herein. On the contrary, the intent is to cover all alternatives, modifications, and equivalents included within the spirit and scope of the invention as defined by the appended claims.

[0022]FIGS. 1 through 19 illustrate various systems, methods, and predefined masks, which are configured to reduce cross-talk between ADSL and other concurrently-deployed services while optimizing ADSL performance. Each of the embodiments maximizes downstream performance, balances upstream and downstream signal ratios, and provides spectral compatibility between ADSL and concurrently-deployed services (e.g., integrated services digital network (ISDN), plain old telephone systems (POTS), etc.). In maximizing downstream performance, the systems and methods are configured to determine the optimum data capacity given certain line conditions (e.g., signal-to-noise ratio (SNR), line attenuation, etc.). The line conditions further provide information that permit the allocation of bandwidths and time slots for upstream and downstream signals, thereby balancing the upstream and downstream signal ratios. Additionally, since the line conditions provide information related to other concurrently-deployed services on the line, the systems and methods of FIGS. 1 through 19 also provide spectral compatibility between ADSL and other concurrently-deployed services. The optimum conditions are predetermined as a function of government regulations, known or measured physical parameters, and other factors that are well known in the art. The data transmission parameters are then adjusted according to the predetermined optimum conditions. Also, unlike prior systems, which typically relied on parameters determined at a network management level, the embodiments of FIGS. 1 through 19 provide systems and methods for determining modem parameters without relying on parameters determined at the network management level.

[0023]FIG. 1 is a block diagram showing an example asymmetric digital subscriber line (ADSL) communication system 100 employing PSD masks selected in response to line conditions. Generally, the ADSL system is implemented between a central office 110 and a customer premise 160. Communication between the two sites 110, 160 takes place over a communication line 155 (also referred to as a local loop, twisted-pair cable, two-conductor pair wire, or channel). The central office 110 end of the communication line 155 is configured to provide broadband services (e.g., video conferencing 115, Internet 120, telephone services 125, movies on demand 130, broadcast media 135, etc.), which are assembled via central office ADSL modems 150 for transmission over the communication line 155. The central office 110 assembles the signals from the broadband services at an ADSL service rack 140, which comprises a digital subscriber line access multiplexer (DSLAM) 145 and ADSL modems 150. The central office 110 assembles the broadband services via the DSLAM 145 for appropriate transformation and transmission by one or more ADSL modems 150. Each of the ADSL modems 150 may be in communication via a dedicated communication line 155 with a suitably configured ADSL modem 180 at a customer premise 160.

[0024] As illustrated in FIG. 1, the DSLAM 145 and each of a plurality of ADSL modems 150 may be assembled within an ADSL service rack 140 within the central office 110. For simplicity of illustration and explanation, the ADSL communication system 100 presented in FIG. 1 is shown with a single ADSL service rack 140 for communicating each of the broadband services to n ADSL modems 150. The ADSL service rack 140 may be configured to supply conditioned resources necessary to support the operation of the n ADSL modems 150. Those skilled in the art will appreciate the scalability of the ADSL communication system 100 generally presented in FIG. 1. For example, the central office 110 may be configured with a plurality of Transmission Control Protocol/Internet Protocol (TCP/IP) routers and Asynchronous Transfer Mode (ATM) switches (not shown) that may distribute one or more broadband service signals to a plurality of DSLAMs 145. In turn, the plurality of DSLAMs 145 may further distribute the broadband service signals to a plurality of remotely located ADSL modems 180.

[0025] At the opposite end of the communication line 155, the customer premise 160 may be configured with a compatible ADSL modem 180, which may be configured to process and distribute the multiple broadband services to appropriate destination devices such as a computer 170, a television 175, and digital telephones 190 as illustrated. It is significant to note that that the customer premise 160 may have plain old telephone systems (POTS) devices such as a facsimile machine 165 and an analog (POTS) telephone 185 integrated on the communication line 155 along with the ADSL modem 180. It is also feasible that the customer premise 160 may be replaced in some applications by another central office 110 or an ADSL repeater, where the POTS service may not be available or needed.

[0026]FIG. 2 is a block diagram showing the ADSL modem 150 of FIG. 5 in greater detail. While FIG. 2 shows only one ADSL modem 150, it should be appreciated that each of the ADSL modems 150 of FIG. 5 may have similar components. As shown in FIG. 2, the ADSL modem 150 at the central office 510 comprises an ADSL transceiver unit (ATU-C) 205 configured to assemble data for transmission on the communication line 155. In this regard, the ATU-C 205 comprises both a fast path and an interleaved path. Both the fast path and the interleaved path interpose a tone ordering circuit 250 and a multiplexing (MUX) and synchronization (sync) control block 210. The fast path, which provides low latency, comprises a fast cyclic redundancy checking (CRC) block 215 and a scrambling and forward error correcting (FEC) block 225. The interleaved path, which provides a lower error rate at a greater latency, comprises an interleaved CRC block 220, a scrambling and FEC block 230, and an interleaver 240. Since MUX/sync control blocks 210, CRC blocks 215, 220, scrambling and FEC blocks 225, 230, interleavers 240, and tone ordering circuits 250 are known in the art, further discussion of these components is omitted here. However, it should be appreciated that the signal, upon traversing either the fast path or the interleaved path, enters an encoding and gain scaling block 255, which encodes the data into a constellation and also scales the data for transmission. The encoding and gain scaling block 255 is discussed in greater detail with reference to FIG. 7.

[0027] Once the data has been encoded and gain-scaled, the data is relayed in parallel blocks to an inverse Fourier transform (IFT) block 260, which performs a IFT on the parallel data blocks. The IFT data is conveyed to a parallel-to-serial (P/S) converter 265, which converts the data into a serial data stream. The serial data stream is conveyed to a digital-to-analog (D/A) converter and analog processor 270, which produces an analog signal for data transmission. Since IFT blocks 260, P/S converters 265, D/A converters and analog processors 270 are known in the art, further discussion of these components is omitted here. The analog signal is transmitted through the communication line 155 by a transmitter 275 in the ATU-C 205.

[0028]FIG. 3 is a block diagram showing logic components in the encoding and gain scaling block 255 of FIG. 2, which is configured to select an appropriate predefined mask in response to line conditions, and encode and gain scale data according to the selected mask. As shown in FIG. 3, the encoder and gain scaler 255 comprises a receiver 310 and a processor 320. The receiver 3 10 is configured to receive data from the tone-ordering circuit 250 as well as signals from the communication line 155.; The signals contain information related to line conditions, which, in turn, are indicative of services deployed on the communication line 155. The signals from the communication line 155 comprise signal-to-noise ratio (SNR) information of the communication line 155, line attenuation information of the communication line 155, and information related to usable sub-carriers in the DMT modulated system. The signals from the communication line 155 are updated for each data frame being encoded and gain scaled. Thus, the encoder and gain scaler 255 is continuously updated with line condition information.

[0029] The processor 320 is configured to adaptively determine line characteristics and select an appropriate predefined mask as a function of the received signal from the communication line 155. In this regard, the processor 320 may be seen as having a plurality of predefined masks 350 that, to a certain extent, determine the operating parameters of the modem. The redefined masks 350 may comprise predefined time-frequency masks 354 (described below with reference to FIGS. 4A through 7), predefined power spectral density (PSD) masks 352 (described below with reference to FIGS. 8 through 18), or a combination of both predefined time-frequency masks 354 and predefined PSD masks 352. In addition to the predefined masks 350, the processor may be seen as having line condition determination logic 330, which is configured to determine line conditions from the received signal, and mask selection logic 340, which is configured to select an appropriate predefined mask 350 in response to the determination of the line condition. The processor 320 may also be seen as having data loading logic 360, which is configured to load data into the various DMT sub-carriers according to the selected predefined mask 350. In one embodiment, the mask selection logic 340 may be further configured to adaptively select different predefined masks 350 in: response to changing line conditions. In another embodiment, the mask selection logic 340 may be further configured to select a predefined mask only during a modem handshake procedure, or at predefined intervals.

[0030] In operation, the receiver 310 receives a signal from the communication line 155, thereby providing information related to line conditions. This signal is relayed to the line condition determination logic 330 in the processor 320, which determines line conditions from the signal. Upon determining the line conditions, the line condition information is relayed to the mask selection logic 340, which selects a predefined mask 350 by correlating the line condition information to an appropriate predefined mask 350. The selected predefined mask 350 is used by the data loading logic 360 to load the DMT sub-carriers with data. The data is then cascaded through the remaining components in the ATU-C 205, as shown in FIG. 2, for transmission across the communication line 155.

[0031] Attention is now turned to FIGS. 4A through 7, which show several embodiments of time-frequency masks 354, each of which may be selected by the mask selection logic 340, either alone or in combination with one of the PSD masks 352 shown in FIGS. 8 through 18.

[0032]FIG. 4A is a graph showing an example of time-frequency masks without overlapping regions between upstream and downstream masks in accordance with one embodiment of the invention. Two graphs are shown in which a downstream allocated time-frequency mask 410 for a central office is shown on the left graph while an upstream allocated time-frequency mask 420 for a customer premises is shown in the right graph. The graphs show frequency plotted on the x-axis 204 and time plotted on the y-axis 202, with a total data transmission time (designated as 100%) 208 divided into a downstream portion 212 (designated as X%) and an upstream portion 206 (designated as (100−X)%). As shown in FIG. 4A, an upstream signal is transmitted from the customer premises during the (100−X)% upstream portion 206 of the total time 208 using only a portion 370 of the entire ADSL bandwidth. Thus, during the (100−X)% upstream portion 206 of the total time 208, a downstream signal may be transmitted by the central office within the unused portion of the entire ADSL bandwidth. Conversely, when there is no upstream signal being transmitted from the customer premises, then a downstream signal may be transmitted using the entire ADSL bandwidth. Thus, in the embodiment of FIG. 4A, the downstream mask may be seen as an adaptive mask, which (1) spans the entire ADSL frequency bandwidth when there are no upstream signals; and (2) spans only a downstream portion of the bandwidth when there are upstream signals.

[0033] More generally, FIG. 4A may be seen as a time-frequency mask in which the bandwidth adaptively changes in response to line characteristics. Thus, FIG. 4A may be seen as a “snapshot” of an adaptively-changing time-frequency mask. In this regard, the downstream allocated time-frequency mask 410 is determined by line characteristics such as line signal-to-noise ratio (SNR) information, line attenuation information, information related to usable sub-carriers (for discrete multi-tone (DMT) modulation systems), etc. Thus, for the specific embodiment of FIG. 4A, the presence of upstream signals produces different line characteristics than the absence of upstream signals, thereby resulting in a greater bandwidth allocation for downstream signals in the absence of upstream signals. Since the determination of line characteristics is described in standards documents such as International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) G.992.2, “Splitterless Asymmetric Digital Subscriber Line (ADSL) Transceivers” (hereinafter “ITU-T G.992.2”) and ITU-T G.994.1, “Handshake Procedures for Digital Subscriber Line (DSL) Transceivers” (hereinafter “ITU-T G.994.1”) both published in June of 1999, further discussion of determination of line characteristics is omitted here. ITU-T G.992.2 and ITU-T G.994.1 are incorporated herein by reference as if set forth in there entireties. It is worthwhile, however, to note that the particular time-frequency mask of FIG. 4A may be selected in response to the line conditions once the line conditions have been determined by known techniques.

[0034]FIG. 4B is a graph showing another example of time-frequency masks without overlapping regions between upstream and downstream masks in accordance with another embodiment of the invention. Again, while a specific embodiment is shown in FIG. 4B, it will be clear to one of ordinary skill in the art that, more generally, FIG. 4B shows another adaptively-changing time-frequency mask. Two graphs are shown in which a downstream allocated time-frequency mask 430 for a central office is shown on the left graph while an upstream allocated time-frequency mask 440 for a customer premises is shown in the right graph. The graphs show frequency plotted on the x-axis 204 and time plotted on the y-axis 202, with a total data transmission time (designated as 100%) 208 divided into a downstream portion 212 (designated as X%) and; an upstream portion 206 (designated as (100−X)%). As shown in FIG. 4B, both the upstream allocated time-frequency mask 440 and the downstream allocated time-frequency mask 430 are shaped such that both the customer premises and the central office, in the aggregate, utilize the entire ADSL frequency bandwidth. In this sense, the downstream allocated time-frequency mask 430 utilizes a first bandwidth 450, 470 (e.g., W+Z kHz) in the absence of upstream signals, while the downstream allocated time-frequency mask 430 utilizes a second bandwidth 470 (e.g., Z kHz) in the presence of upstream signals. Similarly, the upstream allocated time-frequency mask 440 utilizes a first bandwidth 460 (e.g., Y kHz) in the absence of downstream signals, while the upstream allocated time-frequency mask 440 utilizes a second bandwidth 450, 460 (e.g., W+Y kHz) in the presence of downstream signals. Thus, in the embodiment of FIG. 4B, the downstream mask may be seen as an adaptive mask, which (1) spans a first downstream bandwidth 450, 470 when the central office is receiving upstream signals; and (2) spans a second downstream bandwidth 470 when the central office is not receiving upstream signals. Hence, unlike the time-frequency mask of FIG. 4A, the embodiment of FIG. 4B permits shaping of both upstream and downstream time-frequency masks, thereby permitting greater flexibility in data transmission.

[0035]FIG. 4C is a graph showing another example of time-frequency masks without overlapping regions between upstream and downstream masks in accordance with another embodiment of the invention. Again, while a specific embodiment is shown in FIG. 4C, it will be clear to one of ordinary skill in the art that, more generally, FIG. 4C shows another adaptively-changing time-frequency mask. Two graphs are shown in which a downstream allocated time-frequency mask 450 for a central office is shown on the left graph while an upstream allocated time-frequency mask 460 for a customer premises is shown in the right graph. Specifically, the time-frequency mask of FIG. 4C is referred to as a “zipper mask” due to the configuration of allocated bandwidth. The graphs show frequency plotted on the x-axis 204 and time plotted on the y-axis 202, with a total data transmission time (designated as 100%) 208. As shown in FIG. 4C, both the upstream allocated time-frequency mask 460 and the downstream allocated time-frequency mask 450 are shaped such that both the customer premises and the central office, in the aggregate, utilize the entire ADSL frequency bandwidth. In this sense, the downstream allocated time-frequency mask 450 utilizes two bandwidths 450, 470 (e.g., W+Z kHz), while the downstream allocated time-frequency mask 450 utilizes a different bandwidth 460 (e.g., Y kHz). While the snapshot view of the time-frequency mask shows a static view at a particular time, it will be clear that the two downstream bandwidths 450, 470 and the different upstream bandwidth 460 may shrink or expand as a function of determined line characteristics.

[0036]FIG. 5 is a graph showing an example of time-frequency masks having overlapping regions between upstream and downstream masks in accordance with another embodiment of the invention. Again, while a specific embodiment is shown in FIG. 5, it will be clear to one of ordinary skill in the art that, more generally, FIG. 5 shows another adaptively-changing time-frequency mask. In the embodiment of FIG. 5, an echo cancellation scheme is used, thereby permitting an upstream bandwidth to overlap with a downstream bandwidth. Two graphs are shown in which a downstream allocated time-frequency mask 410 for a central office is shown on the left graph while an upstream allocated time-frequency mask 510 for a customer premises is shown in the right graph. The graphs show frequency plotted on the x-axis 204 and time plotted on the y-axis 202. As shown in FIG. 5, allocation of an upstream bandwidth; is independent of allocation of a downstream bandwidth. Thus, during a portion of the time (X%) 212, both upstream and downstream signals may be transmitted using the same bandwidth 370. Additionally, during another portion of the time (100−X%) 206, only upstream signals may be transmitted within that bandwidth 370. Since overlap modes, such as echo-cancellation modes, are well known in the art, further discussion of such modes are omitted here. It is, however, worthwhile to note that echo-cancellation or overlap modes permit a more efficient use of bandwidth in lieu of increased complexity and costs.

[0037]FIG. 6 is a graph showing an example of time-frequency masks having partially-overlapping regions between upstream and downstream masks in accordance with another embodiment of the invention. As shown in FIG. 6, both the upstream time-frequency mask 610 and the downstream time-frequency mask 620 are loaded with dual bit-mapped data. Since dual bit-mapping schemes are known in the art, only a cursory description of dual bit-mapping is presented here.

[0038] In digital communication systems (e.g., systems employing discrete multi-tone (DMT) modulation schemes), the number of bits that may be loaded into discrete sub-carriers (or bins) is determined as a function of a desired bit-error rate (BER) and a measured signal-to-noise ratio (SNR). Generally, for a given BER, a greater SNR permits greater data capacity (i.e., greater data loading). Conversely, a reduced SNR results in reduced data capacity. For systems employing a single bit-mapping scheme, the data capacity is determined for the worst possible SNR, and various sub-carriers (or bins) are loaded with data as a function of the determined data capacity. Thus, for single bit-mapping systems, the same data-loading scheme is used regardless of whether or not there is overlap between the upstream and downstream time-frequency masks. In this regard, for single bit-mapping systems, the data-loading scheme for non-overlapping regions of the time-frequency mask is the same as for the overlapping regions of the time-frequency mask even when there may be available capacity for more data.

[0039] In the embodiment of FIG. 6, a dual bit-mapping scheme is shown for both the upstream time-frequency mask 620 and the downstream time-frequency mask 610. In this regard, a first data-loading scheme is used in the upstream bandwidth 650 during the overlapping time 630 and a different data-loading scheme is used in the upstream bandwidth 650 during the non-overlapping time 640. This dual bit-mapping scheme results in a greater data capacity for upstream signals. Similarly, different data-loading schemes are used for the downstream time-frequency mask 610 during the overlapping time 630 than during the non-overlapping time 640. In this regard, the dual bit-mapping scheme of FIG. 6 permits greater data capacity for both upstream and downstream signals.

[0040]FIG. 7 is a graph showing an example of time-frequency division multiplexing with overlapping regions between upstream and downstream masks, in accordance with another embodiment of the invention. Unlike FIG. 6, which showed both upstream and downstream signals being loaded using a dual bit-mapping scheme, FIG. 7 shows the downstream signals being loaded using a dual bit-mapping scheme while the upstream signals are loaded using a single bit-mapping scheme. Since much of the inefficiency in signal transmission resides with downstream signal transmission, the dual bit-mapping of downstream signals greatly increases the efficiency in overall signal transmission. Since dual bit-mapping schemes are discussed with reference to FIG. 6, further discussion of dual bit-mapping schemes is omitted here. It is, however, worthwhile to note that due to the dual bit-mapping scheme of the downstream allocated time-frequency mask 710, a greater data capacity is achievable for downstream signals in the presence of non-stationary noise.

[0041] Attention, is now turned to FIGS. 8 through 18, which show several embodiments of PSD masks 352, each of which may be selected by the mask selection logic 340.

[0042]FIG. 8 is a diagram showing one embodiment of a PSD mask 352 selected by the mask selection logic 340 of FIG. 3. As shown in FIG. 8, the PSD mask 352 is defined by power levels of approximately −97.5 dBm/Hz peak below approximately 4 kHz; approximately $\left( {{- 92.5} + {21 \times {\log_{2}\left( \frac{f}{4} \right)}}} \right)$

[0043] dBm/Hz between approximately 4 kHz and approximately 26 kHz; approximately −36.5 dBm/Hz between approximately 26 kHz and approximately 1104 kHz; approximately $\left( {{- 36.5} - {36 \times {\log_{2}\left( \frac{f}{1104} \right)}}} \right)$

[0044] between approximately 1104 kHz and approximately 3093 kHz; approximately −90 dBm/Hz above approximately 3093 kHz, with no greater than approximately −50 dBm power in any 1 MHz sliding window above approximately 4545 kHz. Specifically, the PSD mask 352 shown in FIG. 8 is configured to optimize downstream performance, balance downstream and upstream signal ratios, and provide spectral compatibility in Annex A systems. Since Annex A systems are known in the art and discussed in greater detail in G.992.1, further discussion of Annex A systems is omitted here.

[0045]FIG. 9 is a diagram showing one embodiment of a PSD mask 352 selected by the mask selection logic 340 of FIG. 3. As shown in FIG. 9, the PSD mask 352 is defined by power levels of approximately −97.5 dBm/Hz below approximately 4 kHz; approximately $\left( {{- 92.5} + {4.63 \times {\log_{2}\left( \frac{f}{4} \right)}}} \right)$

[0046] dBm/Hz between approximately 4 kHz and approximately 80 kHz; approximately $\left( {{- 72.5} + {36 \times {\log_{2}\left( \frac{f}{80} \right)}}} \right)$

[0047] dBm/Hz between approximately 80 kHz and approximately 138 kHz; approximately −36.5 dBm/Hz between approximately 138 kHz and approximately 1104 kHz; approximately $\left( {{- 36.5} - {36 \times {\log_{2}\left( \frac{f}{1104} \right)}}} \right)$

[0048] between approximately 1104 kHz and approximately 3093 kHz; and approximately −90 dBm/Hz above approximately 3093 kHz, with no greater than approximately −50 dBm power in any 1 MHz sliding window above approximately 4545 kHz. Specifically, the PSD mask 352 shown in FIG. 9 is configured to optimize downstream performance, balance downstream and upstream signal ratios, and provide spectral compatibility in reduced near-end cross-talk (NEXT) Annex A systems. Since Annex A systems are known in the art and discussed in greater detail in G.992.1, further discussion of Annex A systems is omitted here.

[0049]FIG. 10A is a diagram showing one embodiment of a PSD mask 352 selected by the mask selection logic 340 of FIG. 3. As shown in FIG. 10A, the PSD mask 352 is defined by power levels of approximately −90 dBm/Hz below approximately 50 kHz; approximately $\left( {{- 90} + {12 \times {\log_{2}\left( \frac{f}{50} \right)}}} \right)$

[0050] dBm/Hz between approximately 50 kHz and approximately 80 kHz; a variable power level between approximately 80 kHz and approximately 138 kHz; approximately −36.5 dBm/Hz between approximately 138 kHz and approximately 1104 kHz; approximately $\left( {{- 36.5} - {36 \times {\log_{2}\left( \frac{f}{1104} \right)}}} \right)$

[0051] between approximately 1104 kHz and approximately 3093 kHz; and approximately −90 dBm/Hz above approximately 3093 kHz, with no greater than approximately −50 dBm power in any 1 MHz sliding window above approximately 4545 kHz. Specifically, the PSD mask 352 shown in FIG. 10A is configured to optimize downstream performance, balance downstream and upstream signal ratios, and provide spectral compatibility in ADSL/ISDN Annex B systems employing two-binary-one-quaternary (2B1Q) encoding. Since these systems are known in the art and discussed in greater detail in G.992.1, further discussion of Annex B systems and 2B1Q is omitted here.

[0052]FIG. 10B is a diagram showing one embodiment of a PSD mask 352 selected by the mask selection logic 340 of FIG. 3. As shown in FIG. 10B, the PSD mask 352 is defined by power levels of approximately −90 dBm/Hz below approximately 70 kHz; approximately $\left( {{- 90} + {12 \times {\log_{2}\left( \frac{f}{70} \right)}}} \right)$

[0053] dBm/Hz between approximately 70 kHz and approximately 90 kHz; a variable power level between approximately 90 kHz and approximately 138 kHz; approximately −36.5 dBm/Hz between approximately 138 kHz and approximately 1104 kHz; approximately $\left( {{- 36.5} - {36 \times {\log_{2}\left( \frac{f}{1104} \right)}}} \right)$

[0054] between approximately 1104 kHz and approximately 3093 kHz; and approximately −90 dBm/Hz above approximately 3093 kHz, with no greater than approximately −50 dBm power in any 1 MHz sliding window above approximately 4545 kHz. Specifically, the PSD mask 352 shown in FIG. 10B is configured to optimize downstream performance, balance downstream and upstream signal ratios, and provide spectral compatibility in ADSL/ISDN Annex B systems employing four-binary-three-ternary (4B3T) encoding. Since these systems are known in the art and discussed in greater detail in G.992.1, further discussion of Annex B systems and 4B3T is omitted here.

[0055]FIG. 11 is a diagram showing one embodiment of a PSD mask 352 selected by the mask selection logic 340 of FIG. 3. As shown in FIG. 11, the PSD mask 352 is defined by power levels of approximately −97.5 dBm/Hz below approximately 4 kHz; approximately $\left( {{- 97.5} + {17.8 \times {\log_{2}\left( \frac{f}{4} \right)}}} \right)$

[0056] dBm/Hz between approximately 4 kHz and approximately 26 kHz; approximately −36.5 dBm/Hz between approximately 26 kHz and approximately 121 kHz; approximately $\left( {{- 49.5} - {78.24 \times {\log_{2}\left( \frac{f}{121} \right)}}} \right)$

[0057] dBm/Hz between approximately 121 kHz and approximately 151 kHz; approximately −74.5 dBm/Hz between approximately 151 kHz and approximately 164 kHz; approximately −36.5 dBm/Hz between approximately 164 kHz and approximately 1104 kHz; approximately $\left( {{- 36.5} - {36 \times {\log_{2}\left( \frac{f}{1104} \right)}}} \right)$

[0058] between approximately 1104 kHz and approximately 3093 kHz; and approximately −90 dBm/Hz above approximately 3093 kHz. Specifically, the PSD mask 352 shown in FIG. 11 is configured to optimize downstream performance, balance downstream and upstream signal ratios, and provide spectral compatibility in Annex A and Annex C systems employing a FEXT bit-mapping (FBM) scheme. Since these systems are known in the art, further discussion of such systems is omitted here.

[0059]FIG. 12 is a diagram showing one embodiment of a PSD mask 352 selected by the mask selection logic 340 of FIG. 3. As shown in FIG. 12, the PSD mask 352 is defined by power levels of approximately −97.5 dBm/Hz below approximately 4 kHz; approximately $\left( {{- 97.5} + {17.8 \times {\log_{2}\left( \frac{f}{4} \right)}}} \right)$

[0060] dBm/Hz between approximately 4 kHz and approximately 26 kHz; approximately −36.5 dBm/Hz between approximately 26 kHz and approximately 121 kHz; approximately $\left( {{- 49.5} - {115.8 \times {\log_{2}\left( \frac{f}{121} \right)}}} \right),$

[0061] dBm/Hz between approximately 121 kHz and approximately 151 kHz; approximately −85.5 dBm/Hz between approximately 151 kHz and approximately 164 kHz; approximately −36.5 dBm/Hz between approximately 164 kHz and approximately 1104 kHz; approximately $\left( {{- 36.5} - {36 \times {\log_{2}\left( \frac{f}{1104} \right)}}} \right)$

[0062] between approximately 1104 kHz and approximately 3093 kHz; and approximately −90 dBm/Hz above approximately 3093 kHz. Specifically, the PSD mask 352 shown in FIG. 12 is configured to optimize downstream performance, balance downstream and upstream signal ratios, and provide spectral compatibility in systems employing shaped-overlapping spectra.

[0063]FIG. 13 is a diagram showing one embodiment of a PSD mask 352 selected by the mask selection logic 340 of FIG. 3. As shown in FIG. 13, the PSD mask 352 is defined by power levels of approximately −97.5 dBm/Hz below approximately 4 kHz; approximately $\left( {{- 97.5} + {17.8 \times {\log_{2}\left( \frac{f}{4} \right)}}} \right)$

[0064] dBm/Hz between approximately 4 kHz and approximately 26 kHz; approximately −36.5 dBm/Hz between approximately 26 kHz and approximately 147 kHz; approximately −41.5 dBm/Hz between approximately 147 kHz and approximately 164 kHz; approximately −36.5 dBm/Hz between approximately 164 kHz and approximately 1104 kHz; approximately $\left( {{- 36.5} - {36 \times {\log_{2}\left( \frac{f}{1104} \right)}}} \right)$

[0065] between approximately 1104 kHz and approximately 3093 kHz; and approximately −90 dBm/Hz above approximately 3093 kHz. Specifically, the PSD mask 352 shown in FIG. 13 is configured to optimize downstream performance, balance downstream and upstream signal ratios, and provide spectral compatibility in Annex C systems.

[0066]FIG. 14 is a diagram shoving one embodiment of a PSD mask 352 selected by the mask selection logic 340 of FIG. 3. As shown in FIG. 14, the PSD mask 352 is defined by power levels of approximately −97.5 dBm/Hz below approximately 4 kHz; approximately −94.5 dBm/Hz between approximately 4 kHz and approximately 31 kHz; approximately $\left( {{- 94.5} + {10.88 \times {\log_{2}\left( \frac{f}{31} \right)}}} \right)$

[0067] dBm/Hz between approximately 31 kHz and approximately 104 kHz; approximately $\left( {{- 75.5} + {96.54 \times {\log_{2}\left( \frac{f}{104} \right)}}} \right)$

[0068] dBm/Hz between approximately 104 kHz and approximately 134 kHz; approximately $\left( {{- 40.2} + {9.6 \times {\log_{2}\left( \frac{f}{134} \right)}}} \right)$

[0069] dBm/Hz between approximately 134 kHz and approximately 175 kHz; approximately −36.5 dBm/Hz between approximately 175 kHz and approximately 1104 kHz; approximately $\left( {{- 36.5} - {36 \times {\log_{2}\left( \frac{f}{1104} \right)}}} \right)$

[0070] between approximately 1104 kHz and approximately 3093 kHz; and approximately −90 dBm/Hz above approximately 3093 kHz. Specifically, the PSD mask 352 shown in FIG. 14 is configured to optimize downstream performance, balance downstream and upstream signal ratios, and provide spectral compatibility in the presence of NEXT in extended-reach systems employing time-frequency division duplexing.

[0071]FIG. 15 is a diagram showing one embodiment of a PSD mask 352 selected by the mask selection logic 340 of FIG. 3. As shown in FIG. 15, the PSD mask 352 is defined by power levels of approximately −97.5. dBm/Hz below approximately 4 kHz; approximately −94.5 dBm/Hz between approximately 4 kHz and approximately 24 kHz; approximately $\left( {{- 80} + {18.42 \times {\log_{2}\left( \frac{f}{24} \right)}}} \right)$

[0072] dBm/Hz between approximately 24 kHz and approximately 43 kHz; approximately $\left( {{- 64.5} + {18 \times {\log_{2}\left( \frac{f}{43} \right)}}} \right)$

[0073] dBm/Hz between approximately 43 dBm/Hz and approximately 74 kHz; approximately $\left( {{- 50.4} + {14.24 \times {\log_{2}\left( \frac{f}{74} \right)}}} \right)$

[0074] dBm/Hz between approximately 74 kHz and approximately 121 kHz; approximately $\left( {{- 40.3} + {7.61 \times {\log_{2}\left( \frac{f}{121} \right)}}} \right)$

[0075] dBm/Hz between approximately 121 kHz and approximately 171 kHz; approximately −36.5 dBm/Hz between approximately 171 kHz and approximately 1104 kHz; approximately $\left( {{- 36.5} - {36 \times {\log_{2}\left( \frac{f}{1104} \right)}}} \right)$

[0076] between approximately 1104 kHz and approximately 3093 kHz; and approximately −90 dBm/Hz above approximately 3093 kHz. Specifically, the PSD mask 352 shown in FIG. 15 is configured to optimize downstream performance, balance downstream and upstream signal ratios, and provide spectral compatibility in the presence of FEXT in extended-reach systems employing time-frequency division duplexing.

[0077]FIG. 16 is a diagram showing one embodiment of a PSD mask 352 selected by the mask selection logic 340 of FIG. 3. As shown in FIG. 16, the PSD mask 352 is defined by power levels of approximately −97.5 dBm/Hz below approximately 4 kHz; approximately −86.5 dBm/Hz between approximately 4 kHz and approximately 10 kHz; approximately $\left( {{- 86.5} + {25.8 \times {\log_{2}\left( \frac{f}{10} \right)}}} \right)$

[0078] dBm/Hz between approximately 10 kHz and approximately 27 kHz; approximately $\left( {{- 49.5} + {9.46 \times {\log_{2}\left( \frac{f}{27} \right)}}} \right)$

[0079] dBm/Hz between approximately 27 kHz and approximately 70 kHz; approximately −36.5 dBm/Hz between approximately 70 kHz and approximately 1104 kHz; approximately $\left( {{- 36.5} - {36 \times {\log_{2}\left( \frac{f}{1104} \right)}}} \right)$

[0080] between approximately 1104 kHz and approximately 3093 kHz; and approximately −90 dBm/Hz above approximately 3093 kHz. Specifically, the PSD mask 352 shown in FIG. 16 is configured to optimize downstream performance, balance downstream and upstream signal ratios, and provide spectral compatibility in the presence of FEXT in systems employing a FBM scheme.

[0081]FIG. 17 is a diagram showing one embodiment of a PSD mask 352 selected by the mask selection logic 340 of FIG. 3. As shown in FIG. 17, the PSD mask 352 is defined by power levels of approximately −97.5 dBm/Hz below approximately 4 kHz; approximately $\left( {{- 97.5} + {11 \times {\log_{2}\left( \frac{f}{4} \right)}}} \right)$

[0082] dBm/Hz between approximately 4 kHz and approximately 50 kHz; approximately $\left( {{- 57.5} + {15.7 \times {\log_{2}\left( \frac{f}{50} \right)}}} \right)$

[0083] dBm/Hz between approximately 50 kHz and approximately 126 kHz; approximately −36.5 dBm/Hz between approximately 126 kHz and approximately 1104 kHz; approximately $\left( {{- 36.5} - {36 \times {\log_{2}\left( \frac{f}{1104} \right)}}} \right)$

[0084] between approximately 1104 kHz and approximately 3093 kHz; and approximately −90 dBm/Hz above approximately 3093 kHz. Specifically, the PSD mask 352 shown in FIG. 17 is configured to optimize downstream performance, balance downstream and upstream signal ratios, and provide spectral compatibility in the presence of FEXT in systems employing time-frequency division duplexing.

[0085]FIG. 18 is a diagram showing one embodiment of a PSD mask 352 selected by the mask selection logic 340 of FIG. 3. As shown in FIG. 18, the PSD mask 352 is defined by power levels of approximately −97.5 dBm/Hz below approximately 4 kHz; approximately −94.5 dBm/Hz between approximately 4 kHz and approximately 32 kHz; approximately $\left( {{- 94.5} + {20.65 \times {\log_{2}\left( \frac{f}{32} \right)}}} \right)$

[0086] dBm/Hz between approximately 32 kHz and approximately 109 kHz; approximately $\left( {{- 58} + {58 \times {\log_{2}\left( \frac{f}{109} \right)}}} \right)$

[0087] dBm/Hz between approximately 109 kHz and approximately 138 kHz; approximately $\left( {{- 38.3} + {3.36 \times {\log_{2}\left( \frac{f}{138} \right)}}} \right)$

[0088] dBm/Hz between approximately 138 kHz and approximately 200 kHz; approximately −36.5 dBm/Hz between approximately 200 kHz and approximately 1104 kHz; approximately $\left( {{- 36.5} - {36 \times {\log_{2}\left( \frac{f}{1104} \right)}}} \right)$

[0089] between approximately 1104 kHz and approximately 3093 kHz; and approximately −90 dBm/Hz above approximately 3093 kHz. Specifically, the PSD mask 352 shown in FIG. 18 is configured to optimize downstream performance, balance downstream and upstream signal ratios, and provide spectral compatibility in the presence of NEXT in systems employing time-frequency division duplexing.

[0090] Having described various time-frequency masks 354 and various PSD masks 352 that may be used to improve data transmission in accordance with several embodiments of the invention, attention is turned to FIG. 19, which shows one embodiment of a method for improving data transmission. As shown in FIG. 19, a signal is received (1920) from a communication line 155. The received (1920) signal includes information indicative of line conditions, such as line signal-to-noise ratio (SNR) information, line attenuation information, usable sub-carrier information, bother concurrently deployed services, etc. Upon receiving (1920) the signal, a predefined mask is selected (1930) using the information from the received (1920) signal, In an example embodiment, as shown in FIG. 19, the predefined mask may be adaptively selected as a function of changing line conditions. However, in other embodiments, the predefined mask may be selected during a modem handshake procedure or other predetermined times. The predefined mask may be one of the time-frequency masks shown in FIGS. 4A through 7, one of the power spectral density (PSD) masks shown in FIGS. 8 through 18, or a combination of a time-frequency mask and a PSD mask. It should, however, be appreciated that any predefined mask may be selected. In this regard, the particular shape of the predefined mask may be determined as a function of government regulations, known or measured physical parameters, and other factors that are well known in the art. Upon selecting (1930) a predefined mask, sub-carriers are loaded (1940) with data as a function of the selected (1930) predefined mask. It should be appreciated that the sub-carriers may be loaded (1940) using a single bit-mapping scheme, a dual bit-mapping scheme, a far-end cross-talk (FEXT) bit-mapping (FBM) scheme, or any analogous data-loading, scheme known in the art.

[0091] The line condition determination logic 330, the mask selection logic 340, and the data loading logic 360 of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the preferred embodiment(s), the line condition determination logic 330, the mask selection logic 340, and the data loading logic 360 is implemented in hardware using any or a combination of the following technologies, which are all well known in the art: a discrete logic circuit(s) having logic gates for implementing logic functions upon data signals, an application specific integrated circuit (ASIC) having appropriate combinational logic gates, a programmable gate array(s) (PGA), a field programmable gate array (FPGA), etc. In an alternative embodiment, the line condition determination logic 330, the mask selection logic 340, and the data loading logic 360 is implemented in software or firmware that is stored in a memory and that is executed by a suitable instruction execution system.

[0092] Any process descriptions or blocks in flow charts should be understood as representing modules, segments, or portions of code which include one or more executable instructions for implementing specific logical functions or steps in the process, and alternate implementations are included within the scope of the preferred embodiment of the present invention in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art of the present invention.

[0093] Although an exemplary embodiment of the present invention has been shown and described, it will be apparent to those of ordinary skill in the art that a number of changes, modifications, or alterations to the invention as described may be made, none of which depart from the spirit of the present invention. For example, while the PSD masks 352 and time-frequency masks 354 are shown, in FIG. 3 as being included as hardware components, it should be appreciated that these predefined masks 350 maybe stored in memory (not shown) at a location separate from the processor 320, and accessed by the mask selection logic 340 as needed. Also, while FIGS. 4A through 18 show various time-frequency masks 354 and various PSD masks 352, it should be understood that the invention is not limited to the specifically described predefined masks 350. Conversely, the invention should be seen as encompassing any time-frequency mask or PSD mask that is predefined and stored for subsequent access by the mask selection logic 340. Also, while many of the PSD masks 352 in FIGS. 8 through 18 are shown as static masks, it should be appreciated that the static masks may also be replaced by adaptively-changing masks that adaptively change power levels in various frequency ranges as a function of changing line conditions. Similarly, while the example embodiments of FIGS. 1 through 19 show adaptive selection of predefined masks 350, it should be appreciated that a predefined mask may be selected in response to a modem handshake procedure and, thereafter, remain static until a subsequent modem handshake procedure. Also, it should be appreciated that, while a greater effect is realized in shaping of downstream signals, the invention is equally applicable to upstream data transmission. Moreover, while certain PSD masks are shown to have approximately −90 dBm/Hz above approximately 3093 kHz, it should be understood that the power levels above approximately 3093 kHz for these PSD masks may also include a limitation that the power level not exceed approximately −50 dBm power in any 1 MHz sliding window above approximately 4545 kHz.

[0094] All such changes, modifications, and alterations should therefore be seen as within the scope of the present invention. 

We claim:
 1. A method for improving data transmission in a discrete multi-tone (DMT) modulated asymmetric digital subscriber line (ADSL) system, the method comprising: receiving a signal from a communication line, the signal having information indicative of line conditions, the information indicative of line conditions comprising: line signal-to-noise ratio (SNR) information; line attenuation information; and information related to usable sub-carriers; determining line conditions from the received signal, the line conditions comprising information related to concurrently-deployed services; and adaptively selecting a predefined mask in response to the determined line conditions, the adaptively selecting the predefined mask comprising: comparing the line conditions to predefined parameters; and correlating the predefined parameters to a predefined mask.
 2. The system of claim 1, wherein the predefined mask is a predefined time-frequency mask.
 3. The system of claim 1, wherein the predefined mask is a predefined power spectral density (PSD) mask.
 4. A system for improving data transmission, comprising: predefined masks; a receiver configured to receive a signal from a communication line, the signal having information indicative of line conditions; and logic configured to select one of the predefined masks in response to the received signal from the communication line.
 5. The system of claim 4, further comprising data loading logic configured to load sub-carriers with data.
 6. The system of claim 5, wherein the data loading logic is further configured to load the sub-carriers using a single bit-mapping scheme.
 7. The system of claim 5, wherein the data loading logic is further configured to load the sub-carriers using a dual bit-mapping scheme.
 8. The system of claim 4, wherein the logic configured to select one of the predefined masks is further configured to adaptively select one of the predefined masks in response to changing line conditions.
 9. The system of claim 4, wherein the predefined masks comprise: predefined time-frequency masks; predefined power spectral density (PSD) masks; and a combination of a predefined time-frequency mask and a predefined PSD mask.
 10. The system of claim 9, wherein the predefined time-frequency masks include a time-frequency mask comprising: a time slot allocated to carry downstream signals, wherein the time slot is configured to adaptively change in response to line characteristics; and a frequency bandwidth allocated to carry the downstream signals, wherein the frequency bandwidth is configured to adaptively change in response to the line characteristics.
 11. The system of claim 9, wherein the predefined PSD masks include an adaptively-filtered PSD mask having a portion configured to adaptively change in response to line characteristics.
 12. The system of claim 11, wherein the adaptively-changing portion is defined by a fixed frequency range having a variable attenuation.
 13. The system of claim 11, wherein the adaptively-changing portion is defined by a changing frequency range having a fixed attenuation.
 14. The system of claim 11, wherein the adaptively-changing portion is defined by a changing frequency range having a variable attenuation.
 15. The system of claim 9, wherein the predefined PSD mask is defined by power levels of: approximately −97.5 dBm/Hz peak below approximately 4 kHz; approximately $\left( {{- 92.5} + {21 \times {\log_{2}\left( \frac{f}{4} \right)}}} \right)$

dBm/Hz between approximately 4 kHz and approximately 26 kHz; approximately −36.5 dBm/Hz between approximately 26 kHz and approximately 1104 kHz; approximately $\left( {{- 36.5} - {36 \times {\log_{2}\left( \frac{f}{1104} \right)}}} \right)$

between approximately 1104 kHz and approximately 3093 kHz; approximately −90 dBm/Hz above approximately 3093 kHz, with no greater than approximately −50 dBm power in any 1 MHz sliding window above approximately 4545 kHz.
 16. The system of claim 9, wherein the predefined PSD mask is defined by power levels of: approximately −97.5 dBm/Hz below approximately 4 kHz; approximately $\left( {{- 92.5} + {4.63 \times {\log_{2}\left( \frac{f}{4} \right)}}} \right)$

dBm/Hz between approximately 4 kHz and approximately 80 kHz; approximately $\left( {{- 72.5} + {36 \times {\log_{2}\left( \frac{f}{80} \right)}}} \right)$

dBm/Hz between approximately 80 kHz and approximately 138 kHz; approximately −36.5 dBm/Hz between approximately 138 kHz and approximately 1104 kHz; approximately $\left( {{- 36.5} - {36 \times {\log_{2}\left( \frac{f}{1104} \right)}}} \right)$

between approximately 1104 kHz and approximately 3093 kHz; and approximately −90 dBm/Hz above approximately 3093 kHz, with no greater than approximately −50 dBm power in any 1 MHz sliding window above approximately 4545 kHz.
 17. The system of claim 9, wherein the predefined PSD mask is defined by power levels of: approximately −90 dBm/Hz below approximately 50 kHz; approximately $\left( {{- 90} + {12 \times {\log_{2}\left( \frac{f}{50} \right)}}} \right)$

dBm/Hz between approximately 50 kHz and approximately 80 kHz; a variable power level between approximately 80 kHz and approximately 138 kHz; approximately −36.5 dBm/Hz between approximately 138 kHz and approximately 1104 kHz; approximately $\left( {{- 36.5} - {36 \times {\log_{2}\left( \frac{f}{1104} \right)}}} \right)$

between approximately 1104 kHz and approximately 3093 kHz; and approximately −90 dBm/Hz above approximately 3093 kHz, with no greater than approximately −50 dBm power in any 1 MHz sliding window above approximately 4545 kHz.
 18. The system of claim 9, wherein the predefined PSD mask is defined by power levels of: approximately −90 dBm/Hz below approximately 70 kHz; approximately $\left( {{- 90} + {12 \times {\log_{2}\left( \frac{f}{70} \right)}}} \right)$

dBm/Hz between approximately 70 kHz and approximately 90 kHz; a variable power level between approximately 90 kHz and approximately 138 kHz; approximately −36.5 dBm/Hz between approximately 138 kHz and approximately 1104 kHz; approximately $\left( {{- 36.5} - {36 \times {\log_{2}\left( \frac{f}{1104} \right)}}} \right)$

between approximately 1104 kHz and approximately 3093 kHz; and approximately −90 dBm/Hz above approximately 3093 kHz, with no greater than approximately −50 dBm power in any 1 MHz sliding window above approximately 4545 kHz.
 19. The system of claim 9, wherein the predefined PSD mask is defined by power levels of: approximately −97.5 dBm/Hz below approximately 4 kHz; approximately $\left( {{- 97.5} + {17.8 \times {\log_{2}\left( \frac{f}{4} \right)}}} \right)$

dBm/Hz between approximately 4 kHz and approximately 26 kHz; approximately −36.5 dBm/Hz between approximately 26 kHz and approximately 121 kHz; approximately $\left( {{- 49.5} - {78.24 \times {\log_{2}\left( \frac{f}{121} \right)}}} \right)$

dBm/Hz between approximately 121 kHz and approximately 151 kHz; approximately −74.5 dBm/Hz between approximately 151 kHz and approximately 164 kHz; approximately −36.5 dBm/Hz between approximately 164 kHz and approximately 1104 kHz; approximately $\left( {{- 36.5} - {36 \times {\log_{2}\left( \frac{f}{1104} \right)}}} \right)$

between approximately 1104 kHz and approximately 3093 kHz; and approximately −90 dBm/Hz above approximately 3093 kHz.
 20. The system of claim 9, wherein the predefined PSD mask is defined by power levels of: approximately −97.5 dBm/Hz below approximately 4 kHz; approximately $\left( {{- 97.5} + {17.8 \times {\log_{2}\left( \frac{f}{4} \right)}}} \right)$

dBm/Hz between approximately 4 kHz and approximately 26 kHz; approximately −36.5 dBm/Hz between approximately 26 kHz and approximately 121 kHz; approximately $\left( {{- 49.5} - {115.8 \times {\log_{2}\left( \frac{f}{121} \right)}}} \right)$

dBm/Hz between approximately 121 kHz and approximately 151 kHz; approximately −85.5 dBm/Hz between approximately 151 kHz and approximately 164 kHz; approximately −36.5 dBm/Hz between approximately 164 kHz and approximately 1104 kHz; approximately $\left( {{- 36.5} - {36 \times {\log_{2}\left( \frac{f}{1104} \right)}}} \right)$

between approximately 1104 kHz and approximately 3093 kHz; and approximately −90 dBm/Hz above approximately 3093 kHz.
 21. The system of claim 9, wherein the predefined PSD mask is defined by power levels of. approximately −97.5 dBm/Hz below approximately 4 kHz; approximately $\left( {{- 97.5} + {17.8 \times {\log_{2}\left( \frac{f}{4} \right)}}} \right)$

dBm/Hz between approximately 4 kHz and approximately 26 kHz; approximately −36.5 dBm/Hz between approximately 26 kHz and approximately 147 kHz; approximately −41.5 dBm/Hz between approximately 147 kHz and approximately 164 kHz; approximately −36.5 dBm/Hz between approximately 164 kHz and approximately 1104 kHz; approximately $\left( {{- 36.5} - {36 \times {\log_{2}\left( \frac{f}{1104} \right)}}} \right)$

between approximately 1104 kHz and approximately 3093 kHz; and approximately −90 dBm/Hz above approximately 3093 kHz.
 22. The system of claim 9, wherein the predefined PSD mask is defined by power levels of: approximately −97.5 dBm/Hz below approximately 4 kHz; approximately −94.5 dBm/Hz between approximately 4 kHz and approximately 31 kHz; approximately $\left( {{- 94.5} + {10.88 \times {\log_{2}\left( \frac{f}{31} \right)}}} \right)$

dBm/Hz between approximately 31 kHz and approximately 104 kHz; approximately $\left( {{- 75.5} + {96.54 \times {\log_{2}\left( \frac{f}{104} \right)}}} \right)$

dBm/Hz between approximately 104 kHz and approximately 134 kHz; approximately $\left( {{- 40.2} + {9.6 \times {\log_{2}\left( \frac{f}{134} \right)}}} \right)$

dBm/Hz between approximately 134 kHz and approximately 175 kHz; approximately −36.5 dBm/Hz between approximately 175 kHz and approximately 1104 kHz; approximately $\left( {{- 36.5} - {36 \times {\log_{2}\left( \frac{f}{1104} \right)}}} \right)$

between approximately 1104 kHz and approximately 3093 kHz; and approximately −90 dBm/Hz above approximately 3093 kHz.
 23. The system of claim 9, wherein the predefined PSD mask is defined by power levels of: approximately −97.5 dBm/Hz below approximately 4 kHz; approximately −94.5 dBm/Hz between approximately 4 kHz and approximately 24 kHz; approximately $\left( {{- 80} + {18.42 \times {\log_{2}\left( \frac{f}{24} \right)}}} \right)$

dBm/Hz between approximately, 24 kHz and approximately 43 kHz; approximately $\left( {{- 64.5} + {18 \times {\log_{2}\left( \frac{f}{43} \right)}}} \right)$

dBm/Hz between approximately 43 kHz and approximately 74 kHz; approximately $\left( {{- 50.4} + {14.24 \times {\log_{2}\left( \frac{f}{74} \right)}}} \right)$

dBm/Hz between approximately 74 kHz and approximately 121 kHz; approximately $\left( {{- 40.3} + {7.61 \times {\log_{2}\left( \frac{f}{121} \right)}}} \right)$

dBm/Hz between approximately 121 kHz and approximately 171 kHz; approximately −36.5 dBm/Hz between approximately 171 kHz and approximately 1104 kHz; approximately $\left( {{- 36.5} - {36 \times {\log_{2}\left( \frac{f}{1104} \right)}}} \right)$

between approximately 1104 kHz and approximately 3093 kHz; and approximately −90 dBm/Hz above approximately 3093 kHz.
 24. The system of claim 9, wherein the predefined PSD mask is defined by power levels of: approximately −97.5 dBm/Hz below approximately 4 kHz; approximately −86.5 dBm/Hz between approximately 4 kHz and approximately 10 kHz; approximately $\left( {{- 86.5} + {25.8 \times {\log_{2}\left( \frac{f}{10} \right)}}} \right)$

dBm/Hz between approximately 10 kHz and approximately 27 kHz; approximately $\left( {{- 49.5} + {9.46 \times {\log_{2}\left( \frac{f}{27} \right)}}} \right)$

dBm/Hz between approximately 27 kHz and approximately 70 kHz; approximately −36.5 dBm/Hz between approximately 70 kHz and approximately 1104 kHz; approximately $\left( {{- 36.5} - {36 \times {\log_{2}\left( \frac{f}{1104} \right)}}} \right)$

between approximately 1104 kHz and approximately 3093 kHz; and approximately −90 dBm/Hz above approximately 3093 kHz.
 25. The system of claim 9, wherein the predefined PSD mask is defined by power levels of: approximately −97.5 dBm/Hz below approximately 4 kHz; approximately $\left( {{- 97.5} + {11 \times {\log_{2}\left( \frac{f}{4} \right)}}} \right)$

dBm/Hz between approximately 4 kHz and approximately 50 kHz; approximately $\left( {{- 57.5} + {15.7 \times {\log_{2}\left( \frac{f}{50} \right)}}} \right)$

dBm/Hz between approximately 50 kHz and approximately 126 kHz; approximately −36.5 dBm/Hz between approximately 126 kHz and approximately 1104 kHz; approximately $\left( {{- 36.5} - {36 \times {\log_{2}\left( \frac{f}{1104} \right)}}} \right)$

between approximately 1104 kHz and approximately 3093 kHz; and approximately −90 dBm/Hz above approximately 3093 kHz.
 26. The system of claim 9, wherein the predefined PSD mask is defined by power levels of: approximately −97.5 dBm/Hz below approximately 4 kHz; approximately −94.5 dBm/Hz between approximately 4 kHz and approximately 32 kHz; approximately $\left( {{- 94.5} + {20.65 \times {\log_{2}\left( \frac{f}{32} \right)}}} \right)$

dBm/Hz between approximately 32 kHz and approximately 109 kHz; approximately $\left( {{- 58} + {58 \times {\log_{2}\left( \frac{f}{109} \right)}}} \right)$

dBm/Hz between approximately 109 kHz and approximately 138 kHz; approximately $\left( {{- 38.3} + {3.36 \times {\log_{2}\left( \frac{f}{138} \right)}}} \right)$

dBm/Hz between approximately 138 kHz and approximately 200 kHz; approximately −36.5 dBm/Hz between approximately 200 kHz and approximately 1104 kHz; approximately $\left( {{- 36.5} - {36 \times {\log_{2}\left( \frac{f}{1104} \right)}}} \right)$

between approximately 1104 kHz and approximately 3093 kHz; and approximately −90 dBm/Hz above approximately 3093 kHz.
 27. A method for improving data transmission comprising: receiving a signal from a communication line, the signal having information indicative of line conditions; and selecting a predefined mask in response to the received signal.
 28. A method for improving data transmission comprising: receiving a signal from a communication line, the signal having information indicative of line conditions; and adaptively selecting a predefined mask in response to the received signal.
 29. The method of claim 28, further comprising loading sub-carriers with data as a function of the adaptively-selected predefined mask.
 30. The method of claim 29, wherein the loading sub-carriers with data comprises loading the sub-carriers using a single bit-mapping scheme.
 31. The method of claim 29, wherein the loading sub-carriers with data comprises loading the sub-carriers using a dual bit-mapping scheme.
 32. The method of claim 28, wherein the adaptively selecting the predefined mask comprises adaptively selecting a predefined time-frequency masks.
 33. The method of claim 28, wherein the adaptively selecting the predefined mask comprises adaptively selecting a predefined power spectral density (PSD) masks.
 34. The method of claim 28, wherein the adaptively selecting the predefined mask comprises adaptively selecting a combination of a predefined time-frequency mask and a predefined power spectral density (PSD) mask.
 35. A system for improving data transmission comprising: means for receiving a signal from a communication line, the signal having information indicative of line conditions; and means for selecting a predefined mask in response to the received signal.
 36. The system of claim 35, further comprising means for loading sub-carriers with data as a function of the selected predefined mask. 